Dual-cycle signal amplification on an Au@CeO2-x/Bi2MoO6 platform: Toward an ultrasensitive and enzyme-free sandwich immunosensor for CA125 in clinical diagnostics.

The early detection of ovarian cancer biomarkers is essential for effective diagnosis, calling for highly sensitive and reliable immunosensing platforms. In this work, we present a dual-cycle amplified sandwich-type electrochemical immunosensor for the detection of Carbohydrate Antigen 125 (CA125), a key biomarker of ovarian cancer. The sensing platform was fabricated by immobilizing the primary antibody (Ab1) on a glassy carbon electrode modified with Au@GO-Chi-Fc nanocomposite. A catalytic probe was prepared by conjugating the secondary antibody (Ab2) with gold nanoparticles anchored on Ce-doped Bi2MoO6 nanoflowers (Au@CeO2-x/Bi2MoO6). These probes efficiently catalyze the reduction of p-nitrophenol (p-NP) to p-aminophenol (p-AP), which subsequently triggers an electrocatalytic chemical (ECC) redox cycling reaction with NaBH4, leading to significant signal amplification. This enzyme-free strategy provides the immunosensor with an ultra-wide linear range (0.0005-100 U mL-1) and an ultralow detection limit (0.00049 U mL-1), enabling accurate quantification of CA125 in diverse human serum samples. Moreover, the immunosensor demonstrates high selectivity, excellent reproducibility, and stable performance over 18 days, underscoring its robustness and clinical potential for the detection of trace CA125 in complex biological matrices.